One intradialytic symptom is the disequilibrium syndrome which was first described in 1961. The disequilibrium syndrome is a set of systemic and neurologic symptoms that can occur either during or soon after dialysis. Early symptoms are nausea, vomiting, restlessness and headache, followed by seizures, obtundation and coma. Some believe that the cause is related to an acute increase in brain water content, while others believe that the cause relates to acute changes in the pH of the cerebrospinal fluid during dialysis. This problem is exacerbated when acute patients with very high plasma urea nitrogen values are subject to a dialysis which is too efficient.
The treatment for mild symptoms is to decrease the efficiency of the solute removal and pH changes, such as by reducing the blood flow. Hypertonic NaCl or glucose can also be administered.
With more severe symptoms, the dialysis session should be stopped. Intravenous mannitol may also be of benefit.
The disequilibrium syndrome can be avoided by using high NaCl concentrations of at least 140 mmol/l and by using glucose concentrations of at least 200 mg/dl. Decreasing the sodium dialysis solution during dialysis treatment has also been suggested.
Another common intradialytic complication is symptomatic hypotension, which is normally related to an excessively rapid decrease in the blood volume during dialysis. Today most dialysis machines use a volume control for ultrafiltration, which is a method which aids in preventing symptomatic hypotension. Other methods include the profiling of sodium, use of low temperature, switching from acetate to bicarbonate, etc.
Furthermore, ultrafiltration below the patient's dry weight may result in symptomatic hypotension associated with, for instance, cramps, dizziness, malaise and a washed-out feeling.
An object of the present invention is to solve these and related intradialytic complications during dialysis.
Biofeedback is a subject which is being investigated by many researchers. One example is U.S. Pat. No. 4,469,593 which discloses a blood purification apparatus including a hematocrit measurement apparatus. The hematocrit value is used for controlling a negative ultrafiltration pressure on the dialysate side of a dialyzer for maintaining the hematocrit value constant or according to a pre-defined profile. Also the conductivity of the blood or plasma is used in order to establish an upper limit for sodium, while the hematocrit value controls both the addition of replacement fluid and for increasing the sodium concentration in a hemofiltration apparatus. Finally, the oncotic pressure is also used for biofeedback.
International Patent No. WO 94/08641 discloses an on-line real time urea sensor which is used to measure the urea concentration in the effluent from a dialyzer. The system establishes two exponential fits of the urea concentration, with an early fit during the first 30 minutes and a late fit during the flowing treatment time. By obtaining an initial BUN-value, the Kt/V or SRI (solute removal index) can be calculated and projected to the intended time. In this way, the efficiency of the treatment can be measured on line. It is stated that the efficiency decreases at all times during the treatment time, although presumably more slowly at the end. It is also stated that deviation from a projected Kt/V value can be used for troubleshooting.
International Patent No. WO 95/32010 discloses a method of determining the optimum blood flow (as measured by pump speed) in order to obtain the most efficient dialysis. It is observed that the efficiency or clearance of the dialyzer is dependent on the blood flow rate (and dialysis flow rate, as well as temperature, etc.). However, above a predetermined blood flow, the efficiency of the dialyzer once again decreases. There are several factors for this phenomenon, one of which is fistula recirculation. According to International Patent No. WO 95/32010, the efficiency of the dialyzer is determined at different blood flows, for example in increments of 50 ml/min, and the blood flow at maximum clearance is used. The maximum blood flow is determined at the start of each treatment. If this maximum blood flow declines after a number of weeks or days, it can be a sign of fistula malfunction. In this specification, a urea sensor is used for assessing the efficiency of the treatment at the start.